The use of a voice coil motor driving circuit in the field of magnetic disk drive units is well known in the prior art. A typical voice coil motor driving circuit has retracting function in which a read/write head of the disk drive unit can be retraced from a memory portion of the magnetic disk when disk operation is ceased or power is shut off. In the prior art it is common practice to include additional power supply such as a battery in a voice coil motor driving circuit with retracting function, for the purpose of supplying power to a retract control circuit which controls a retract current flowing through a voice coil motor. This additional battery requires additional cost and space in the voice coil motor driving circuit.